The present invention relates to a circuit configuration which is intended for a brake system with anti-lock control and/or traction slip control and which comprises (a) circuits for conditioning sensor signals representative of the rotational behavior of the individual vehicle wheels, (b) controller circuits for analyzing and processing the conditioned sensor signals and for generating braking pressure control signals that drive solenoid valves inserted into the pressure fluid conduits of the brake system, (c) monitoring circuits to which the conditioned sensor signals can be supplied and which, in case of a malfunction, de-activate or disconnect the control in part or completely, and (d) circuits for exchanging and comparing signals of the controller circuits with corresponding signals of the monitoring circuits.
A circuit configuration for controlling and monitoring an anti-lock brake system is disclosed in patent specification DE 32 34 637 C2. According to this patent specification, the conditioned wheel sensor signals are analyzed and processed in parallel in two completely identical microcontrollers which operate pursuant to the same program and to which the conditioned sensor signals are supplied. The output signals of the two microcontrollers and internal signals or intermediate results are exchanged and compared. Since the two controllers are supplied with the same sensor signals, the external and the internal signals must be coincident when the system is intact. This criterion is assessed for monitoring the system. Once a non-coincidence is detected, this leads to a partial or complete de-activation of the anti-lock control.
The prior art system described above requires two high-quality microcontrollers, although one single microcontroller would be sufficient for generating the actual braking pressure control signals. Consequently, the expenditure in microcontrollers is doubled according to this patent for safety reasons.
An anti-lock brake system, disclosed in published patent application DE 29 28 981 A1, comprises at least one control microcomputer and another microcomputer for testing and monitoring the control channels. By means of this test microcomputer, test signals are generated and delivered into the control channels through the input circuits associated with the control microcomputers. Control operations are simulated by the test signals, and the reaction of the control computer to these simulated signals is sensed. The precondition for the test operations is that no braking with anti-lock control takes place and that the vehicle speed is in excess of a predetermined limit value. Further, for the error detection during braking with anti-lock control, the test microcomputer serves to check the duration of some control signals and of some valve-excitation signals for preserving limit values. Finally, all automatic checking of the microcomputer is provided.
In spite of the relatively great expenditure, naturally, a like arrangement permits only detection of specific errors or types of errors because, in contrast to the circuit configuration described above, redundant signal processing in conjunction with a comparison of the redundantly processed signals for coincidence is not performed.